wasm_export.h: Use "default" visibility

[midokura-xavi92]

Since the top-level CMakelists.txt is appending -fvisibility=hidden to the compile options, no public symbols are exported by default. This forbids users from linking against the shared library.

Using gcc/clang attributes 1, it is possible to override the definition for WASM_RUNTIME_API_EXTERN so that only required symbols are correctly exported.

• Before the patch:

$ nm build/libiwasm.so | grep -e 'wasm_runtime_get_version'
00000000000419e9 t wasm_runtime_get_version

• After the patch:

$ nm build/libiwasm.so | grep -e 'wasm_runtime_get_version'
0000000000043c69 T wasm_runtime_get_version

[lum1n0us]

Please review the changes at #3655. I trust you'll find the information useful.

[midokura-xavi92]

Please review the changes at #3655. I trust you'll find the information useful.

Despite these concerns, I have successfully built this branch i.e., without any undefined references. Is there anything else I should take into account?

As far as I understand, functions such as os_mmap or b_memcpy_s are built from different executables or libraries, so they remain unaffected by iwasm_static or iwasm_shared and the visibility of their symbols. In other words, relevant CMakeLists.txt would include (${SHARED_DIR}/utils/uncommon/shared_uncommon.cmake) directly so as to import the source files that define such symbols.

[lum1n0us]

@bnason-nf @yamt Please review this. Ensure that it does not conflict with your previous plans.

[lum1n0us]

LGTM

[bnason-nf]

Thanks for the heads up @lum1n0us. I think this should be ok, but I would need to test more to be sure. I think it's fine to merge and we can revisit later if it causes any problems for me.

[yamt]

@bnason-nf @yamt Please review this. Ensure that it does not conflict with your previous plans.

honestly speaking, i don't remember the previous discussion well.
this patch itself looks reasonable to me.

@midokura-xavi92 if you care these stuff, you might want to improve the CI coverage.
iirc, our CI coverage on shared library and relevant things is pretty low.
cf. #3687